<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        *{
            padding: 0;
            margin: 0;
        }
        #uls{
            width: 500px;
            height: 500px;
            margin: 50px auto;
        }
        li{
            width: 150px;
            height: 150px;
            background: skyblue;
            float: left;
            list-style: none;
            margin:5px;
            color: #fff;
            text-align: center;
            line-height: 150px;
            font-size: 20px;
            font-weight: bold;
        }
        #uls li button{
            width: 50px;
            height: 30px;
        }
        .light{
            width: 150px;
            height: 150px;
            background: #666;
            color: #fff;
        }
    </style>
</head>
<body>
    <ul id='uls'>
        <li>600元优惠券</li>
        <li>800元优惠券</li>
        <li>1000元优惠券</li>
        <li>800元优惠券</li>
        <li><button id='btn1'>开始</button> <button id='btn2'>停止</button></li>
        <li>600元优惠券</li>
        <li>600元优惠券</li>
        <li>1000元优惠券</li>
        <li>800元优惠券</li>
    </ul>
    <script>
        var btn1=document.getElementById("btn1");
        var btn2=document.getElementById("btn2");
        var arr=[0,1,2,5,8,7,6,3];//按这个下标依次旋转
        var lis=document.getElementsByTagName("li");
        var num=0;  //定义初识下标
        btn1.onclick=function(){
            btn1.disabled=true;
            time=setInterval(function(){
                lis[arr[num]].className="";
                num++;
                if(num>7){
                    num=0;
                }
                lis[arr[num]].className="light";
            },50)
        }
        btn2.onclick=function(){
            btn1.disabled=false;
            clearInterval(time);
        }
    </script>
</body>
</html
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